This invention relates to a seal member for preventing fan air loss through the fan blade root structure in a turbojet compressor section and, more particularly, the invention is concerned with providing a blade seal arrangement including a thin flexible ribbon-like seal having a thickened wedge-shaped portion along its longitudinal center in contact with the gap between two adjacent blade platforms and impelled into the gap during operation of the compressor fan. The seal is fixedly attached to one of the adjacent blade platforms and the thickened portion of the seal includes invaginations which close as the wedge portion fills the gap between the blade platforms.
Heretofore it has been the common practice in certain types of turbojet engines to provide thin flexible seals between adjacent platforms of the composite fan blades. One side of the seal is fixedly attached by cementing or the like to one of the blade platforms while the other side hangs loose over the gap so that when the fan starts to rotate the seal is centrifuged across the gap producing an effective seal. This arrangement is satisfactory where the gap is relatively narrow as in the F101 engine. However, where the gap is wide, the loose side of the thin seal is centrifuged through the gap. When this happens, the seal is ineffective and protrudes into the air stream. If this type of seal of constant thickness were made thick enough to function properly, the added stiffness and unwanted weight would outweigh the advantages obtained.
In the F103, the composite fan blade is required to swing about its root minor axis at least 15.degree. counterclockwise (looking forward) during bird impact and a 5.degree. clockwise swing back following impact. Since the blade platform is attached to the blade, adjacent platforms must clear each other as one blade swings relative to an adjacent blade. This requires a significant gap between adjacent platforms which make up the fan air stream inner flowpath between blades. To minimize fan air loss, the gap must be filled during normal fan operations, but must still allow relative movement between platforms when bird strikes occur. The seal need not remain functional after a severe bird strike. The thin constant thickness F101 seal previously described will not operate in a satisfactory manner with the wide gap required in the F103 engine.